Semi-conductive device for reducing distortion in electron optics



June 3, 1969 w. HEIMANN ET AL 3,448,317

SEMI-CONDUCTIVE DEvIcE FOR REDUCING DISTORTION IN ELECTRON OPTICS FiledMarch 23, 1966 h ALTER HE/Mfl/l A/ & 770 S 66 522157? INVENTORS av yififiZi/mf United States Patent 3,448,317 SEMI-CONDUCTIVE DEVICE FORREDUCING DISTORTION IN ELECTRON OPTICS Walter Heimann,Wiesbaden-Dotzheim, and Otto Scherzer, Darmstadt-Niederramstadt,Germany, assignors to W. Hiemann, doing business asForschungslaboratorium, Prof. Dr.-Iug. W. Heimann, Wieshaden-Dotzheim,Germany Filed Mar. 23, 1966, Ser. No. 541,910 Claims priority,application Germany, Mar. 26, 1965, 45 635 Int. Cl. H013 29710, 31/26,39/00 US. Cl. 313-89 11 Claims ABSTRACT OF THE DISCLOSURE The presentinvention relates to a semi-conducting support for use with electronoptics, and more particularly to such a support which is to be combinedwith a photocathode.

When it is desired to reproduce a plane surface by means of an electronoptics, or electronic lenses, aberration results which causes increasingdefocusing and loss of sharpness and resolution toward the edge of thescreen. The reason for this aberration is, that the axial beams are muchshorter than the beams directed to the edges of the screen. To avoidthis difliculty, it has been proposed to form the screen on a surfacewhich is concave with respect to the cathode. This reduces thedifficulties and increases the sharpness. On the other hand, if opticalirivestigation of the screen is then desired, for example if the surfaceis a photo cathode of an electron-optical image converter, the lightoptics must be designed for a curved surface, which is expensive anddifficult. To obtain depth of field, the aperture available must bedecreased and thus the light intensity available for observation islimited. It is also possible to form a fluorescent screen with a curvedsurface, to reduce aberration, which, however, again substantiallyincreases the difiiculty with optical observation of the screen.

Proposals to change the electron optics, in order to in fiuence thesharpness of the images at the edges of the screen, have not resulted inpractical solutions.

It is an object of the present invention to provide a semi-conductingsupport for the cathode, by which edge aberration and unsharpness isavoided.

Briefly, in accordance with the present invention, a semi-conductingsupport of said carrier plate for use in combination with electronoptics is formed on a carrier plate, and an electrical potential isapplied thereover in a radial direction by electrodes applied as layersand separated except at their center by an insulating or semiconductingmaterial. At least one of the electrode layers is transparent andextends over the surface and is arranged in such a way, or is of suchmaterial and it has a predetermined resistance, so that a potentialgradient is established in a radial direction, from the edge of thesurface or screen toward-s the center where the electrodes are connectedtogether, when the electrodes are connected to a source of potential.The potential drop at the center Patented June 3, 1969 is thus differentfrom the potential drop at the edge, by

a few volts.

The potential drop from the edge of the center may be linear, ornon-linear with respect to radial distance. A photo emission cathode maybe applied directly over the electrode layer, or the electrode layeritself may be of a material which has the desired photo cathode effects,besides having the resistant characteristic-s above referred to. Inorder to avoid a shadow of a lead from the center of the support plate,one of the electrodes can be formed as a transparent screen layer,separated from the other electrode or the resistance material by aninsulating layer from which a center has been left off, for example bymasking, so that the electrodes come together at the center for anelectrical connection avoids the shadow otherwise resulting from a leadto the center.

By suitably choosing the specific resistance of the layers applied tothe surface of the support plate, an appropriate potential drop isobtained to the layer and aberations can be avoided; by making thepotential drop nonlinear, it is also possible to introduce,artificially, desired distortions.

The transparent conductive layers may be tin oxide, SnO as an insulatinglayer, SiO, silicon oxide, or SiO may be used, which are evaporated onthe support plate.

The structure, organization and operation of the invention will now bedescribed more specifically in the following detailed description withreference to the accompanying drawings, in which:

FIG. 1 illustrates, in schematic form, an electron-optical imagetransducer and, in FIG. 1a, the kind of distortion observable;

FIG. 2 shows an image converter similar to FIG. 1 with a concave cathodeand, in FIG. 2a, the image to be desired;

FIG. 3 is a vertical cross sectional view through an arrangement of thescreen in accordance with the present invention;

FIG. 4 is a partial plan view of the central portion of the screen inFIG. 3; and

FIG. 5 illustrates, in schematic form, a screen in accordance with amodified form of the invention.

Referring now to the drawings: the electron-optical transducing systemcomprises, generally, an electronic system 20, and an optical system 30.An electronic image 21 (FIG. 1) will appear, by projections through anelectronic lens system not further illustrated, as the electronic image22 on the reproduction screen 10. The rays on the margin, 25, having totravel a greater distance than the central rays 24, are imperfectlyfocused and therefore blurr the edge of the image. If the rays from themargin of the cathode pass the other zones of the lens, they cause thedistortion shown in FIG. la.

If now the cathode is made concave, as shown at 11, FIG. 2, then therays all pass through the middle of the lens and the length of travel ofthe axial rays 24 is not much larger than that of the peripheral rays 25and the image 23 will not be distorted, or at least will be distorted toa degree which is much less than that of the system of FIG. 1. Anundistorted graph is shown in FIG. 2a. Of course, if an opticalprojection of the raster 23, as illustrated by the optical system 30, isintended to be done on the curved cathode 11, then difiiculties arisebecause the focus of the optical system 30 will be accurate and sharponly with respect to any particular position along the curved screen 11.To compensate for the differences in distance between axial light beamsand peripheral light beams, extremely complicated and expensive opticshave to be used.

A raster as shown in FIG. 2a can be obtained, in accordance with thepresent invention, with a fiat transducing cathode by imposing aradially extending electrical field thereon. A glass plate which may becircular, for example, has a transparent conductive layer 1 appliedthereto. Layer 1 does not extend to the entire circumference of the diskbut rather only over a portion thereof, up to a metal ring 2 which hasan electrical lead 3a applied thereto, for example by extending throughglass plate 5. A transparent insulating layer 4, for example formed ofSiO or SiO is applied over layer 1, for example by evaporation, in sucha manner that the metallic ring 2 and the conductive layer 1 are justcovered. The insulating layer 4 has a central portion thereof removed;this can be achieved for example, by putting a mask over the center,during evaporation. Preferably, the center aperture of the insulatinglayer 4 is toothed or star shaped as shown in FIG. 4. Thus, anelectrical connection to conductive layer 1 can be established at thecenter.

Transparent conductive layer 1a is then applied over insulating layer 4.Again, layer 1a may be evaporated over the insulating layer. Layer 1a isconnected to a metallic ring 3 arranged at the outside of plate 5, whichring 3 is again connected to connection 3a. An electrical potential,placed between rings 2 and 3 by means of battery 3b, in which ring 2 isconnected to the negative side and ring 3 to the positive, will cause aregularly extending potential gradient to result across the face oflayer 1a. The layers 1, 1a have some resistance. Depending upon thevalue of the potential applied, aberrations as shown in FIG. 1a arecompensated more or less; by making the source 3b variable, completecompensation to obtain a raster in accordance with FIG. 2a can beobtained; by changing the voltage even more, overcompensation, that isdistortion similar again to FIG. 1a but with a bending of beamsinwardly, can be obtained. Layers 1, 4, and 1a can be held very thin, sothin that the difference in thickness (shown exaggerated in FIG. 3) atthe center is not noticeable. Layer 1a, may, in itself, form a photocathode, or have other photo cathode material evaporated thereon orotherwise applied thereto.

Referring to FIG. 5, a transparent conductive layer 8 is again appliedto a glass carrier plate 5, as before. Layer 8 is connected, as beforeto lead 3a, and then to a battery 3b. A semi-conductive layer 7 is thendeposited, for example vapor deposited over layer 8. Semi-conductivelayer 7 has a high resistance layer 6 applied thereover; for purposes ofconnection, a ring 6a may be used, applied over layer 7. The resistancedistribution of layer 6, taken vertically in FIG. 5, need not behomogeneous; on the contrary, the resistance distribution may bearranged in such a manner that when a potential is applied betweenlayers 6 and 8, a suitable potential gradient results which isproportional to the radius in the center of the disk, and non-linear atthe peripheral portion. The nonlinearity can readily be changed byvarying the thickness of the applied layer 6 or of the semi-conductorlayer 7 beneath, or changing the physical composition of either theapplied layer 6, or the semi-conductive layer 7.

Distortion having outwardly bending lines as illustrated in FIG. la canthus be compensated perfectly so that a raster in accordance with FIG.2a is obtained; higher order distortions, which sometime arise and causeundulating lines towards the peripheral region, can, by suitable choiceof the resistance distribution of layer 6 or layer 7, be avoidedentirely, when the distribution of resistance is made non-linear.Particularly, distortions of the fifth Seidel orders can be compensatedin this summer. A desirable potential drop distribution, from the centerportion of the surface toward the edge portion may vary, for example,with the square of the radius.

A suitable material for layers 1, 1a (FIG. 3) or layers 6, 8 (FIG. 5) isSnO A suitable material for semi-conductive layer 7 (FIG. 5) is anelectron-conducting glass.

What is claimed is:

1. Semi-conductive support for use in combination with electron opticscomprising a carrier plate;

first and second separated superposed electrodes applied to a surface ofsaid carrier plate and extending essentially over the entire surface andadapted to be connected to a source of potential;

a layer of insulating material located between said electrodes andcovering said first electrode except for a small center region toinsulate and separate said electrodes from each other, except at thecenter, the unseparated center region of the electrodes forming anelectrical connection between both electrodes to establish, uponconnection of said electrodes to a voltage source, a potential gradientradially between the edge and said center region over the extent of saidsurface.

2. Support as claimed in claim 1, wherein one of said electrodesincludes a composition of material forming a photo cathode.

3. Support as claimed in claim 1, wherein the resistance distributionwith respect to the radial distance from the center of the surface ofthe electrodes establishing the potential gradient has a square lawrelationship so that the potential drop from edge portions to the centerof the surface is substantially proportional to the square of thedistance from the center.

4. Support as claimed in claim 1, wherein the resistance distributionwith respect to the radial distance from the center of the surface ofthe electrodes and establishing the potential gradient is chosen so thatthe potential drop is non-linear and that the edge portions suppressdistortions arising due to higher order aberrations.

5. Support as claimed in claim 1 including a layer of semi-conductivematerial covering one of said electrodes; the other of said electrodesbeing formed by a thin, transparent layer of high resistance materialcovering said layer of semi-conductive material.

6. Support as claimed in claim 1, wherein at least one of saidelectrodes is a transparent, thin conductive layer.

7. Support as claimed in claim 1, wherein said conductive layers includea layer of evaporated SnO 8. Support as claimed in claim 1, wherein saidcarrier plate and said means of establishing potential gradient forms asupport for a photo cathode.

9. Support as claimed in claim 8, wherein the thickness of said highresistance material is non-uniform with respect to the radial distancefrom the center of the surface.

10. Support as claimed in claim 8, wherein the high resistance materialis of non-uniform composition with respect to the radial distance fromthe center of the surface.

11. Support as claimed in claim 8', wherein the layer of semi-conductivematerial covering said first electrode has a non-uniform resistancedistribution with respect to the radial distance from the center of thesurface.

References Cited UNITED STATES PATENTS 3,118,084 1/1964 Havn et al.313-78 X 3,155,872 11/1964 H avn et al. 315-23 3,260,876 7/1966 Manleyet a1. 313-80 X 3,308,330 3/1967 C'harles 313-65 X 3,321,665 5/1967 Dye315-169 2,622,219 12/1962 Schagen 313-65 2,908,835 10/1959 Weimer 313-653,048,728 8/1962 Beurle 313-94 X 3,204,142 8/1965 Dehaan et al 313-65 X3,289,024 11/1966 Dehaan et al 313-65 JOHN W. HUCKERT, Primary Examiner.

A. J. JAMES, Assistant Examiner.

US. Cl. X.R.

